Switching and average models are developed for major three-phase PWM converters.
The models are correct for the case when the voltage sources or capacitors with nonzero parasitic
resistances are placed across the converter dc port or ac terminals. The effects of the parasitic
resistances are described by additional time-varying terms in the average models depending not
only on the duty cycle values, but also on the modulation strategy. For analysis purposes, the
terms due to parasitic resistances can be approximated by their fundamental frequency
components ( dc or line/output frequency).

A new small-signal model in the rotating coordinates is developed for a uniformly sampled
three-phase modulator. The model reveals that the uniform sampling introduces delays in the
control inputs and cross-coupling between the control inputs. Furthermore, the model is time varying
causing the complete small-signal model consisting of the modulator and converter small signal
models in the rotating coordinates to become time-varying. Based on the derived
expressions, the worst-case point for the control design can be identified. A modulation strategy
which reduces delay due to the uniform sampling can be selected. The modulator model is
partially verified experimentally.

Influence of delays due to the uniformly sampled PWM and digital implementation is
investigated in the closed-loop control design for the boost rectifier. Designs of standard control
schemes, consisting of inner current loops and a superimposed voltage loop, are presented and
verified experimentally. They can be extended to other three-phase PWM converters.
A new control algorithm is developed and verified experimentally for power factor
correction (PFC) applications of three-phase PWM rectifiers, where a rectifier is preceded by an
input filter. The algorithm provides output voltage regulation and input displacement factor (IDF)
compensation without resorting to the control of input filter states. It allows separate design of the
input filter and the rectifier closed-loop control. A criterion for small-signal stability of the integrated
system, consisting of the rectifier with output voltage regulation and the input filter, has been
formulated and applied to the buck rectifier with the input filter.